1. Field of the Invention
The present invention relates generally to telecommunications, and particularly to billing SIP-originated communications sessions in an efficient manner.
2. Technical Background
In the context of communications networks, the Session Initiation Protocol (SIP) is an application-layer signaling protocol that has been developed to create, modify, and terminate sessions having one or more users. These sessions include Internet telephone calls, multi-media conferences, and multi-media distribution. SIP has enjoyed wide-spread acceptance as a means for signaling telecommunications services over the Internet since its approval as an official telecommunications standard in 1999.
The main function of SIP is to initiate and terminate interactive communications sessions between users. One requirement of initiating a session involves determining the location of the destination user. The destination user may have a SIP phone at work, a personal computer at both work and home, a non-SIP phone at home, or a mobile phone, among others. A call placed to this user may require the ringing of all devices at once, or there may be call forwarding, or some other feature employed to locate the user. After the destination user is located, SIP conveys the response to the session invitation to the originating user. The response may include either an accept or reject message. If the invitation is accepted the session becomes active. At the conclusion of the session, SIP is used to terminate the session.
The other main function of SIP is to provide the destination user with a description of the session he is being invited to. SIP is not concerned with the details of the session, but does provide information about the protocol used to describe the session. For example, SIP may employ Multipurpose Internet Mail Extension (MIME), the session description protocol (SDP), or some other suitable means to describe the session. SIP can also be used to negotiate a common format to describe a particular session.
One type of telephone call that can be placed by a customer is a call from an IP enabled device to a standard telephone set connected to the Public Switched Telephone Network (PSTN). The IP enabled device communicate to the PSTN via an IP network gateway. The network gateway functions as an interface, providing mediation from a packet switched IP signaling/voice system to the circuit switched, time division multiplexed (TDM) system employed by the PSTN. One problem associated with making these types of calls involves billing. Using SIP signaling, the network gateway receives a call set-up message from the originating SIP client. The call set-up message includes the IP address of the caller, which seems to be a relatively straight-forward way of identifying the entity responsible for paying for the call. Unfortunately, it is relatively easy for fraudulent users with access to a personal computer to insert an incorrect caller identification. Thus, the SIP message itself is not a reliable basis for billing purposes. What is needed is a method for billing SIP phone calls in an efficient way that substantially eliminates fraud.